3D priming technology is a technology based on a computer three-dimensional design model and used to build up and band special materials, such as metal powder, ceramic powder, plastic and cell tissue in a layer-wise manner by means of a laser beam, a hot-melt nozzle etc. via software layered discretization and a numerical control molding system so as to finally mold same by super imposition to manufacture a physical product. Rather than shaping and cutting raw materials for finally obtaining a product in the traditional manufacturing industry by means of machining, such as molding and turn milling, 3D printing converts a three-dimensional physical object into several two-dimensional planes for production by processing and superimposing the materials layer by layer, thereby greatly reducing the complexity of manufacturing. This digital manufacturing mode can directly produce parts of any shape from computer graphic data without needing a complicated process, a large machine tool and massive labor, so that the production can be utilized by a broader range of producers.
At present, molding methods of 3D printing technology are still evolving, and the materials used are also various. Among these molding methods, photo-curing method is relatively mature. Photo-curing method uses the principle that a photosensitive resin is cured after being irradiated by an ultraviolet laser so as to mold the material in an additive way, and has the characteristics of, such as a high molding precision, a good surface finish and a high material utilization.
FIG. 1 shows a basic structure of s photo-curing 3D printing apparatus. Such a 3D printing apparatus 100 comprises a material tank 110 for accommodating a photosensitive resin, an image exposure system 120 for curing the photosensitive resin, and a lifting platform 130 for connecting a molding tool. The image exposure system 120 is located above the material tank 110, and can irradiate a light beam image to enable a layer of the photosensitive resin at the liquid surface of the material tank 110 to be cured. Each time after the image exposure system 120 irradiates the light beam image to enable the layer of the photosensitive resin to be cured, the lifting platform 130 will drive the layer of molded photosensitive resin to move downward slightly, and enable the photosensitive resin to be uniformly spread on a lop surface of the cured workpiece via a blade 131 and to get ready for the next irradiation. The cycle repeats, and a three-dimensional workpiece molded by layer addition will be obtained.
The image exposure system 120 commonly uses a laser molding technique or a digital light procession (DLP) projection technique.
Laser molding technique means pointwise scanning using a laser scanning device. However, due to the property of the photosensitive resin, the laser power cannot be too great, or the resin would be damaged. Therefore, the moving speed of the laser is limited to a few meters to no more than twenty meters per second, causing an excessively slow molding speed.
DLP projection imaging technique is realized by using a digital micromirror device (DMD) to control the reflection of light. The digital micromirror device can be considered as a mirror surface. This mirror is composed of hundreds of thousands or even millions of micromirrors. Each micromirror represents a pixel, and an image is constituted by these pixels. Each micromirror can be independently controlled to decide whether light rays are reflected to a projection lens. Finally, the whole mirror reflects the required light beam image. The application of DMD in 3D printing has many advantages, for example, it can handle ultraviolet light below 400 nm without the concern of damage; however, its limited resolution restricts its development, for example, the maximum resolution commonly used in current DMDs is 1920×1080. However, in 3D printing, this resolution at a usual accuracy of 0.1 mm can only produce an object with an area of 192 mm×108 mm, which significantly limits the application thereof.